1. Field of the Invention
The present invention relates to a method for electrochemical machining of workpieces.
2. Discussion of Background Information
Electrochemical machining (ECM) is a shaping machining method for machining workpieces, which can be advantageously used both in the production of complex surface shapes and/or materials which are difficult to machine. The method makes use of the anodic oxidation of the material to be machined, wherein a working electrode is arranged with spacing to the surface to be machined and an electrolyte is provided in the gap between the surface to be machined and the electrode, so that by applying an electrical potential between electrode and workpiece to be machined, the material of the workpiece is dissolved by anodic oxidation and passes into the electrolyte. A material ablation thus results, which is dependent on the potential ratios in the machining gap. These are in turn influenced by the gap width, so that a three-dimensional shape of the working electrode correspondingly having different spacings of the working electrode to the surface to be machined results in a shape-dependent ablation. The shape of the working electrode may therefore be embossed or imaged in the machined surface.
The electrochemical ablation can be carried out not only continuously, but rather also in pulsed form, wherein a continuous current flow is not set, but rather a plurality of current pulses are executed in succession. Such a method is also referred to as PECM (pulsed electrochemical machining).
During the machining of workpieces made of specific materials, for example, workpieces made of titanium aluminides, so-called starting behavior occurs during the electrochemical machining, which is characterized in that during the initial time of the ablation process, the potential and current values measured over the machining gap change. This can have the result that the machining parameters for the electrochemical machining are set incorrectly. For example, an incorrect setting of the gap width, i.e., of the spacing between the surface to be machined and the electrode surface could thus result, which could lead to poor machining results due to the corresponding effects on the potential distribution in the working gap and therefore on the ablation behavior of the material.
Accordingly, methods were already described in WO 03/099498 A1 and WO 03/099499 A1, the entire disclosures of which are incorporated by reference herein, of how the actual gap width between working electrode and surface to be machined can be determined to achieve the correct setting of the gap width. However, these documents are not concerned with the question of how a corresponding starting phase can be recognized during the electrochemical machining and which measures can be taken to achieve optimum electrochemical machining in the case of a starting phase or a comparable transient phase, to ensure optimum electrochemical machining.
It would therefore be advantageous to be able to provide a method for electrochemical machining of workpieces, in which the presence of a starting phase during the electrochemical machining or of a transient phase of the machining process comparable to a starting phase can be recognized and in which optimum electrochemical machining can also be implemented during a starting phase or a comparable transient phase. The corresponding method is to be able to be carried out simply and reliably at the same time, however.